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  • Microbiological surveillance and parenteral antibiotic use: RESULTS

There were 759 admissions to the CrCU during the study. One-third of patients were admitted from the emergency de­partment, 32% of patients came from the operating room and 35% were transferred to the CrCU from another ward or hospi­tal. A total of 258 (32%) patients received parenteral antimi­crobial therapy during their CrCU stay, including 75 medical, 105 surgical and 78 trauma patients. There were 340 courses of antibiotics administered; 226 were for treatment of infec­tion and 114 were for surgical prophylaxis. The average dura­tion of antimicrobial therapy for all patients included in the audit was 6.7 days (range one to 54 days). The most fre­quently prescribed antibiotic was cefazolin (47% of patients, 1098 g total use), followed by gentamicin (33%, 141 g), ceftri­axone (20%, 255 g), metronidazole (19%, 209 g), clindamycin (19%, 459 g) (Dalacin C, Pharmacia & Upjohn Inc, Mississauga, Ontario), cloxacillin (17%, 1913 g), cefuroxime (16%, 323 g) (Zinacef, Glaxo Canada Inc, Toronto, Ontario), vancomycin (15%, 256 g) (Vancocin, Eli Lilly Canada Inc, Scarborough, Ontario), ampicillin (14%, 1028 g) and tobramy­cin (12%, 81 g) (Table 1). The overall cost of all parenteral anti­biotics during the audit was $57,854.35, which represented 18% of the total drug budget for the CrCU for that year.

The average length of stay for patients receiving antibiotics (10.7±14.7 days) was significantly higher than the length of stay of all patients admitted to the CrCU (4.7±8.0 days) dur­ing this period (P<0.01). There were 6.3 infections treated with antibiotics/100 patient days during the surveillance pe­riod. Of the patients who received antimicrobial therapy, 76% remained in the CrCU for more than 48 h.

When the prophylactic antibiotic use was excluded from the analysis, both the average duration of antibiotic therapy and length of stay increased from 6.7 and 10.7 days to 8.5 (range one to 54) and 13.4 (range one to 146) days, respec­tively. There did not, however, appear to be a significant change in the most frequently prescribed antibiotics.

The indications for antimicrobial therapy as determined by the attending medical staff in the CrCU are as summarized in Table 2. Several patients had more than one infectious diag­nosis. In 34% of the infections treated, no bacterial pathogen was identified. Of the culture results collected, 26.3% were from sterile sites. Of the 30 patients with positive blood cul­tures, 20 patients had a primary bacteremia without a clearly identified source. In addition to the blood cultures, only 11 other cultures were from sterile sites (eg, cerebrospinal fluid [CSF], tissue biopsies, specimens obtained during surgical procedures). Pneumonia accounted for over one-third of the indications for antimicrobial treatment. Of the pneumonias di­agnosed on clinical and radiological features (n=121), micro­biological cultures were obtained from endotracheal tube specimens in all but seven; these seven samples were obtained from bronchoalveolar lavage specimens.

The most common organisms isolated from patients with infection were S aureus (25.6%), followed by Pseudomonas ae­ruginosa (13.5%),Enterococcus species (12.2%),Haemophilus influenzae (10.9%), E coli (10.9%), Enterobacter cloacae (7.7%), other Gram-negative (12.8%) and other Gram-positive organisms (4.5%). In particular, S aureus was the most fre­quently cultured organism (24.5%) from blood, followed by Enterococcus species (13.2%), Pseudomonas species (11.3%), Staphylococcus epidermidis (9.4%) and Candida albicans (9.4%).
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Of all the S aureus isolates recovered from patients who re­ceived parenteral antibiotics in the CrCU, only 5% of the S au- reus strains were methicillin-resistant. There were no VRE or enterococci with high-level aminoglycoside resistance. ES6L or imipenem resistance were not found in Gram-negative ba­cilli. Twenty-nine per cent of the H influenzae isolates were beta-lactamase positive. E coli was found to have the highest antimicrobial resistance, with 41% resistant to ampicillin, 24% resistant to gentamicin and 6% resistant to cefazolin. ForEcoli isolates collected from across the hospital during 1995 to 1996, the antimicrobial resistance rates were similar for ampicillin and cefazolin but not for gentamicin, for which the rate was only 4%. Within the Enterobacteriaceae, there was no resistance to trimethoprim/sulphamethoxazole; one Klebsiella species was resistant to cefazolin; two Citrobacter freundii were resistant to gentamicin, with one also resistant to cipro- floxacin (Cipro, Bayer Inc, Toronto). Of the Pseudomonas spe­cies, 5% were resistant to each of piperacillin (Pipracil, Wyeth Ayerst Canada Inc, Montreal, Quebec), ciprofloxacin and cef­tazidime, and none were resistant to the aminoglycosides. One pseudomonal isolate was resistant to both piperacillin and ceftazidime.

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